Security devices are used for a variety of applications. For example, security devices control access to secured areas by automating the control over door locks. This is useful in a variety of situations, such as hotels in which the security device is part of a hotel room door lock. A card reader positioned near or on the door determines whether a card presented by an individual has appropriate information stored on it to allow access through that door. Upon detecting an appropriate, authorized card, the security device automatically unlocks the door, for example.
A variety of such devices are known and in widespread use. Those skilled in the art have been striving to reduce power consumption by security devices. It has been proposed, for example, to use low power circuitry within security devices.
It has been found desirable to allow such devices to enter a sleep mode in which the devices consume minimal power. One approach at providing a wake-up function includes a capacitive wake-up circuit. One shortcoming of such an arrangement is that any object that appears to be capacitive to the wake-up circuit results in unnecessarily waking up the security device such that it consumes power for at least some time. Waking up the security device more often than necessary undesirably consumes additional power.